It looks like brave developers has got the open source android code and have added multitouch support to android and now you can install it in your T-Mobile G1 (use it on your own risk).

They have also written a demo app which is multi touch version of mobile chrome or default browser in android.

Multi-Touch Browser

This is a patched version of the standard Android WebKit browser that supports multi-touch zooming. JesusFreke has kindly included it in his v1.4 image as described above, and you can get the source/patches here.

Features

Multi-Touch zooming using “pinch” gesture like on the iPhone. Fully working and ready to use for daily browsing.
Some pages are not zoomable (even in the single-touch browser), and all pages have an upper and lower zoom limit. With multi-touch zooming, you are shown a new message when you cannot zoom into or out of a given page, in order to give the user more feedback as to why the pinch gesture isn’t working.
Also contains a patch by JesusFreke to support autorotate of the browser display based on phone orientation. You have to manually enable this in the Prefs.

more here